"It's nice to have those jobs back, but the rate of change is not such that you're going to have a renaissance in the Rust Belt," says Joseph Fuller, a professor at Harvard Business School, who has researched job skill trends.

The gap between job openings and job hires in manufacturing has widened this year. There were 271,000 hires in October, meaning, in theory, about 51,000 manufacturing job openings went unfilled in October.

A few reasons -- both good and bad -- help explain why American factories have plenty of openings but not enough hires.

1. Improving job market: When the job market gains momentum, people start moving jobs, leaving openings that need to be filled. The unemployment rate is down to 4.6% from 10% in 2009 -- a sign that the job market has recovered.

2. Job skills gap: Many employers can't find the workers with advanced job skills required for new types of positions, such as 3D manufacturing or operating complex machinery.

3. Passive recruitment: Some employers post job openings once they see orders for their goods increase. But they may want to be sure the pick-up is here to stay and take a "wait and see" approach before actually hiring a person.

4. Trumped up optimism in manufacturing: Since the election, about 78% of manufacturers are either somewhat, or very, positive about their future outlook, according to the National Association of Manufacturers. That's up from 61% in September. Optimism tends to breed job openings.

The trillion dollar question is whether Trump can bring back loads of manufacturing jobs, as he has promised. Trump's big, $1 trillion infrastructure proposal could be a boon for construction and manufacturing jobs in America. Done right, it would also boost U.S. economic growth.

Optimistic employers may also be betting on Trump's promise to strip away regulations on energy -- a sector that requires lots of parts and equipment supplied by manufacturers.

But not everyone is optimistic. Manufacturing trends can take decades to reverse, and job losses have continued to mount this year.

"Do I really think that's going to change? I guess not...I don't think we're going to see a big increase in manufacturing employment," says Susan Helper, an economics professor at Case Western Reserve University who focuses on manufacturing.